Parentcaster

raising two kids is more than twice as hard as raising one kid

4 kids.

0-1 world changing transition. You find out how selfish you are.

1-2 it's now man defense, but lots of the time they can play together so you and spouse can relax a bit, and you don't have to get all new stuff because you can do hand me downs.

2-3 you're out numbered. You thought you knew what was coming.

You greatly underestimated their power.

This is the next hardest after 0-1

3-4 depending on age gaps they oldest kid is likely ready to be really helpful (bonus point if oldest is a girl)
This is the easiest transition so far.

Life gets really wild sometimes and you feel like your life revolves around them.

You're not that wrong, but if your not giving into their every whim and are diligent about making them part of your squad rather than tiny tyrants or nuisances life just keeps getting better.